I've not used ag but just a small shout out for ack: it's a single Perl file (easy to install, v1.x will work with even antique Perl), it works on weird hardware/OS (no compilation required), it contains its own man-page (ack -man) and is fast enough for typical sysadmin tasks and moderate size codebases.

(Ack also supports the full PCRE syntax but that's less of an issue now rg has -P).

If your work takes you to minority platforms ack is certainly worth keeping in your toolbox.

What file sizes did you have issues with?

I'm using ag inside my source directories and cannot remember it not doing the job.